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A job fulfillment system and method includes a storage module having
article storage and access to the article storage for retrieval of
articles and a unit sortation module that is adapted to receive articles
retrieved from the storage module and sorting those articles into jobs. A
control system includes a storage module controller that is adapted to
control operation of the storage module and a unit sortation module
controller that is adapted to control operation of the unit sortation
module. Both the storage module controller and the unit sortation module
controller have a pending job queue and a priority policy that opens jobs
in the respective pending job queue according to a policy. The unit
sortation controller has a work-in-progress (WIP) controller that limits
orders active in the unit sortation module to not exceed a configured
capability of that module. Incoming jobs to the system are received with
the unit sortation module pending job queue and jobs are activated with
the sortation module controller from the sortation module pending job
queue according to the policy of the sortation module control. Jobs that
are active in the sortation module WIP controller are received with the
storage module pending job queue and are activated with the storage
module controller from the storage module pending job queue according to
the policy of the storage module controller.

1. An order fulfillment system, comprising: a storage module having
article storage and access to the article storage for retrieval of
articles; a unit sortation module adapted to receive articles retrieved
from the storage module and sorting those articles into orders; a control
system comprising a storage module controller that is adapted to control
operation of said storage module and a unit sortation module controller
that is adapted to control operation of said unit sortation module, both
said storage module controller and said unit sortation module controller
having a pending job queue and a priority policy that opens jobs in the
respective pending job queue according to a policy; and said unit
sortation module controller including a work-in-progress (WIP) controller
that limits jobs active in the unit sortation module to not exceed a
configured capability, wherein said sortation module pending job queue is
adapted to receive jobs incoming to the system and the unit sortation
module WIP controller activates jobs from the unit sortation module
pending job queue according to the policy of the unit sortation module
control provided that the job limit of the unit sortation module WIP
controller is not reached and said storage module pending job queue is
adapted to receive jobs that are active in the unit sortation module WIP
controller and the storage module controller activates jobs from the
storage module pending job queue according to the policy of the storage
module control.

2. The order fulfillment system as claimed in claim 1 wherein said
storage module controller including a work-in-progress (WIP) controller
that limits jobs active in the storage module to not exceed another
configured capability and wherein the storage module controller activates
jobs from the storage module pending job queue according to the policy of
the storage module control provided that the job limit of the storage
module WIP controller is not met.

3. The order fulfillment system as claimed in claim 1 wherein the unit
sortation module WIP controller activates jobs according to a number of
articles in the jobs.

4. The order fulfillment system as claimed in claim 1 wherein said
storage module comprises an automated warehouse and includes a storage
and retrieval mechanism that is adapted to store articles to the article
storage and to retrieve articles from the storage to provide access to
that article.

5. The order fulfillment system as claimed in claim 1 including a
material flow system that is adapted to transport articles to said unit
sortation module and a unit induct module that is adapted to receive
articles retrieved by the article storage buffer and induct the articles
to said material flow system.

6. The order fulfillment system as claimed in claim 5 wherein said
material flow system comprises an overhead supported pouch system.

7. The order fulfillment system as claimed in claim 5 including a
plurality of said unit induct modules and a plurality of said unit
sortation modules wherein said material flow system is adapted to convey
articles from any of said unit induct modules to substantially any of
said unit sortation modules.

8. The order fulfillment system as claimed in claim 7 including a
plurality of said storage modules, each of said unit induct modules
receiving articles from one of said storage modules.

9. The order fulfillment system as claimed in claim 2 wherein articles
are stored in receptacles in said storage module and wherein a receptacle
having an article is retrieved in order to retrieve that article.

10. The order fulfillment system as claimed in claim 9 wherein a
receptacle having articles for multiple jobs that are active in said
storage module WIP controller is retrieved once in order to retrieve the
articles for the multiple jobs.

11. The order fulfillment system as claimed in claim 2 wherein said
configured capability is selectable as a function of physical capability
of said unit sortation module and said another configured capability is
selectable as a function of physical capacity of said storage module.

12. The order fulfillment system as claimed in claim 1 wherein said
configured capability is selectable as a function of physical capacity of
said unit sortation module.

13. The order fulfillment system as claimed in claim 1 including a
plurality of pack stations each adapted to receive articles making up an
order sorted by the unit sortation module and facilitate packing of the
articles making up an order.

14. The order fulfillment system as claimed in claim 13 including a pack
sorter between said unit sortation module and said pack stations, wherein
said unit sortation module is adapted to sort articles into groups of
orders and said pack sorter is adapted to sort articles for groups of
orders to articles for individual orders at each of the pack stations.

15. The order fulfillment system as claimed in claim 13 wherein said unit
sortation module comprises a comb sorter having an article input, a
plurality of lanes and at least one diverter that is adapted to divert
articles from said article input to one of said lanes.

16. The order fulfillment system as claimed in claim 15 including a
buffer upstream of said article input.

17. The order fulfillment system as claimed in claim 15 wherein each of
said lanes is adapted to receive a maximum number of orders.

18. The order fulfillment system as claimed in claim 17 wherein the
number of pack stations is greater than or equal to the maximum number of
orders that can be received at each of said lanes.

19. The order fulfillment system as claimed in claim 15 wherein said unit
sortation module controller assigns activated orders to a lane until the
number of orders in that lane reaches its maximum number of orders before
assigning an activated order to a different lane.

20. The order fulfillment system as claimed in claim 15 wherein an order
dispatched from said unit sortation module to one of said pack stations
is subtracted from the number of active orders in the unit sortation
module.

21. The order fulfillment system as claimed in claim 15 wherein said unit
sortation module comprises another comb sorter, said another comb sorter
having another article input, a plurality of other lanes and at least one
other diverter that is adapted to divert articles from said other article
input to one of said another lanes and wherein each of said another lanes
adapted to supply articles to said article input of said comb sorter.

22. The order fulfillment system as claimed in claim 21 wherein each of
said another lanes is adapted to receive a maximum number of orders and
wherein each of said another lanes is adapted to supply articles to said
article input of said comb sorter.

23. The order fulfillment system as claimed in claim 22 wherein each of
said another lanes is adapted to receive a maximum number of orders that
is greater than the number of pack stations.

24. The order fulfillment system as claimed in claim 21 wherein said unit
sortation module controller assigns activated orders to another lane
until the number of orders in that another lane reaches its maximum
number of orders before assigning an activated order to a different
another lane.

25. An order fulfillment system, comprising: a storage module having
article storage and access to the article storage for retrieval of
articles; a unit sortation module adapted to receive articles retrieved
from the storage module and sorting those articles into orders; and a
plurality of pack stations each adapted to receive articles making up an
order sorted by the unit sortation module and facilitate packing of the
articles making up an order, wherein said unit sortation module comprises
a comb sorter having an article input, a plurality of lanes and at least
one diverter that is adapted to divert articles from said article input
to one of said lanes; and a control system comprising a storage module
controller that is adapted to control operation of said storage module
and a unit sortation module controller that is adapted to control
operation of said unit sortation module.

26. The order fulfillment system as claimed in claim 25 wherein each of
said lanes is adapted to receive a maximum number of orders.

27. The order fulfillment system as claimed in claim 26 wherein the
number of pack stations is greater than or equal to the maximum number of
orders that can be received at each of said lanes.

28. The order fulfillment system as claimed in claim 25 wherein said unit
sortation module controller assigns activated orders to a lane until the
number of orders in that lane reaches its maximum number of orders before
assigning an activated order to a different lane.

29. The order fulfillment system as claimed in claim 25 wherein an order
dispatched from said unit sortation module to one of said pack stations
is subtracted from the number of activated orders in the unit sortation
module.

30. The order fulfillment system as claimed in claim 25 including a
buffer upstream of said article input.

31. The order fulfillment system as claimed in claim 25 wherein said unit
sortation module comprises another comb sorter, said another comb sorter
having another article input, a plurality of other lanes and at least one
other diverter that is adapted to divert articles from said other article
input to one of said another lanes and wherein each of said another lanes
is adapted to supply articles to said article input of said comb sorter.

32. The order fulfillment system as claimed in claim 31 wherein each of
said another lanes is adapted to receive a maximum number of orders and
wherein each of said another lanes is adapted to supply articles to said
article input of said comb sorter.

33. The order fulfillment system as claimed in claim 32 wherein each of
said another lanes is adapted to receive a maximum number of orders that
is greater than the number of pack stations.

34. The order fulfillment system as claimed in claim 31 wherein said unit
sortation module controller assigns activated orders to another lane
until the number of orders in that lane reaches its maximum number of
orders before assigning an activated order to a different another lane.

35. The order fulfillment system as claimed in claim 31 including a pack
sorter between said unit sortation module and said pack stations, wherein
said unit sortation module is adapted to sort articles into groups of
orders and said pack sorter is adapted to sort groups of orders to
individual orders at each of the pack stations.

36. An order fulfillment method for use with a storage module having
article storage and access to the article storage for retrieval of
articles and a unit sortation module adapted to receive articles
retrieved from the storage module and sorting those articles into orders,
said method comprising: having a control system comprising a storage
module controller and a unit sortation module controller, both said
storage module controller and said unit sortation module controller
having a pending job queue, a priority policy that opens jobs in the
respective pending job queue according to a policy; said unit sortation
module controller having a work in progress (WIP) controller that limits
jobs active in the unit sortation module to not exceed physical
capability of that module, said unit sortation controller receiving jobs
incoming to the system with said sortation module pending job queue and
activating jobs with the sortation module WIP controller from the
sortation module pending job queue according to the policy of the
sortation module control; and receiving jobs that are active in the unit
sortation module WIP controller with said storage module pending job
queue and activating jobs with the storage module controller from the
storage module pending job queue according to the policy of the storage
module control.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. patent application Ser.
No. 62/422,740, filed on Nov. 16, 2016, the disclosure of which is hereby
incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to order fulfillment systems and
methods and, in particular, to pull-type order fulfillment systems and
methods.

[0003] Order fulfillment of orders placed over the Internet must take
place within a relatively short period of time in order to be
commercially competitive. The same could be said for orders received by
phone, facsimile, or by the mail based on catalog or television-based
merchandizing. Such order fulfillment is known as E-commerce and places
demands on an order fulfillment system to meet such obligations. This is
compounded by the fact that E-commerce usually involves a large number of
small orders (each containing as few as one item in the order) that are
selected from a large number of potential items. Each unique item has a
specific inventory identification, known in the industry as a
stock-keeping unit (SKU). Each item usually bears an optical code, such
as a barcode or radio frequency identification (RFID) tag that identifies
the SKU of the item.

[0004] Traditional wave-based order fulfillment systems rely on batches of
orders and buffers in the material-handling system to accumulate large
quantities of items. This tends to produce unpredictable order cycle
times, even under perfect conditions. This can best be seen in FIG. 5,
which compares a simulation of a typical wave-based system under both
idealized conditions A and real world conditions B. Even under idealized
conditions, a significant number of orders are not fulfilled for 7500
seconds or more than two hours. When exceptions are added to the system
in real world conditions, such as missing inventory, system faults, and
other errors, the simulated order time can extend for up to twice that
amount for some orders.

[0005] While other pull-type order fulfillment systems have been proposed,
such pull-type systems make sure that all items making up an order arrive
at packing within the same time window, but do not necessarily reduce the
order cycle time. Furthermore, known pull-type systems may suffer from
the same real world exceptions that dog the wave-type systems.

SUMMARY OF THE INVENTION

[0006] The present invention fulfills orders very quickly within a
warehouse in a real-time manner with high efficiency and flexibility.
Also, buffering in the material-handling system is kept to a minimum.
While useful even with manual processes, such as picking, the present
invention makes the most of high automation; i.e., automated techniques
for storing, retrieving, and sorting inventory items, or articles making
up a customer order, within the warehouse. Orders can be added to the
system and be provided high priority and urgency without disrupting the
system and while allowing orders to meet shipping windows, if necessary.
As used in the following discussion, the term "job" is intended to refer
to individual request at a module such as an order, an order line, or an
item. The term "work" is intended to refer to one or more jobs. The term
"order" is intended to refer to a job for one customer.

[0007] An order fulfillment system and method, according to an aspect of
the invention, includes a storage module having article storage and
access to the article storage for retrieval of articles and a unit
sortation module that is adapted to receive articles retrieved from the
storage module and sort those articles into orders. A control system
includes a storage module controller that is adapted to control operation
of the storage module and a unit sortation module controller that is
adapted to control operation of the unit sortation module. Both the
storage module controller and the unit sortation module controller have a
pending work or job queue, such as a pending order queue and a priority
policy that activates orders in the respective pending work queue
according to a policy. The unit sortation module controller includes a
work-in-progress (WIP) controller that limits jobs, such as orders,
active in the unit sortation module to not exceed a configured
capability. Incoming jobs to the system are received with the unit
sortation module pending job queue and jobs are activated with the unit
sortation module WIP controller from the unit sortation module pending
job queue according to the policy of the sortation module control,
provided that the job limit of the unit sortation module WIP controller
is not reached. Jobs that are active in the unit sortation module WIP
controller are received with the storage module pending order queue and
are activated with the storage module controller from the storage module
pending order queue according to the policy of the storage module
control.

[0008] The storage module controller may include a work-in-progress (WIP)
controller that limits work or jobs such as orders active in the storage
module to not exceed another configured capability and the storage module
controller may activate jobs from the storage module pending job queue
according to the policy of the storage module control provided that the
job limit of the storage module WIP controller is not met. The unit
sortation module WIP controller may limit activated jobs according to a
number of articles in the jobs. The storage module may be an automated
warehouse and include a storage and retrieval mechanism that is adapted
to store articles to the article storage and to retrieve articles from
article storage to provide access to that article. A material flow system
may be provided that is adapted to convey retrieved articles from the
unit induct module to the unit sortation module. A unit induct module may
be adapted to receive articles retrieved by the article storage buffer
and induct the articles to the material flow system. The material flow
system may be an overhead supported pouch system.

[0009] A plurality of the unit induct modules and a plurality of unit
sortation modules may be provided with the material flow system being
adapted to transfer articles from any of the unit induct modules to any
of the unit sortation modules. A plurality of storage modules may be
provided, with each of the unit induct modules receiving articles from
one of the storage modules.

[0010] Articles may be stored in receptacles in the storage module wherein
a receptacle having an article is retrieved in order to retrieve that
article. A receptacle having articles for multiple jobs that are active
in the storage module WIP controller may be retrieved once in order to
retrieve articles for the multiple jobs.

[0011] A plurality of pack stations may be provided, each adapted to
receive articles making up an order sorted by the unit sortation module
and facilitate packing of the articles making up an order. A pack sorter
may be provided between the unit sortation module and the pack stations.
The unit sortation module is adapted to sort articles into groups of
orders and the pack sorter is adapted to sort groups of orders to
individual orders at each of the pack stations.

[0012] The unit sortation module may be a comb sorter having an article
input, a plurality of sorter lanes and at least one diverter that is
adapted to divert articles from the article input to one of the sorter
lanes. Each of the sorter lanes may be adapted to receive a maximum
number of orders. The number of pack stations may be greater than or
equal to the maximum number of orders that can be received at each sorter
lane. The unit sortation module controller may assign activated orders to
a sorter lane until the number of orders in that lane reaches its maximum
number of orders before assigning an activated order to a different lane.
An order dispatched from the unit sortation module to one of the pack
stations may be subtracted from the number of activated orders in the
unit sortation module.

[0013] The unit sortation module may include another comb sorter. The
another comb sorter has another article input, a plurality of other
sorter lanes and at least one other diverter that is adapted to divert
articles from the other article input to one of said another sorter
lanes. Each of the other sorter lanes may be adapted to receive a maximum
number of orders and may be adapted to supply articles to the article
input of the downstream comb sorter. Each of the other lanes' maximum
number of orders may be greater than the number of pack stations. The
unit sortation module controller may assign activated orders to one of
the other lanes until the number of orders in that lane reaches its
maximum number of orders before assigning an activated order to a
different another lane.

[0014] These and other objects, advantages and features of this invention
will become apparent upon review of the following specification in
conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a block diagram of an order fulfillment system and method
according to an embodiment of the invention;

[0016] FIG. 2 is a more detailed block diagram of the order fulfillment
system and method embodiment shown in FIG. 1;

[0017] FIG. 3 is yet a more detailed block diagram of a portion of the
order fulfillment system and method shown in FIGS. 1 and 2;

[0018] FIG. 4 is a block diagram of the order fulfillment system and
method in FIG. 1 illustrating information flow and article flow in the
order fulfillment system and method;

[0019] FIG. 5 is a cycle time histogram simulation of order fulfillment
time distribution in a prior art order fulfillment system and method;

[0020] FIG. 6 is a cycle time histogram simulation of an order fulfillment
time distribution of an order fulfillment system according to embodiments
of the present invention;

[0021] FIG. 7 is a schematic diagram of a single-stage comb unit sortation
module; and

[0023] Referring now to the drawings and the illustrative embodiment
depicted therein, an order fulfillment system 10 includes a storage
module 12 and a unit sortation module 18 (FIGS. 1-3). Storage module 12
has article storage and access to the article storage for retrieval of
articles. In the illustrated embodiment, storage module 12 is an
automated warehouse, such as a Dematic Multishuttle.RTM. system which is
a multi-tier automated warehouse of the type disclosed in commonly
assigned U.S. Pat. No. 8,974,168, the disclosure of which is hereby
incorporated herein by reference in its entirety, or a unit load or ASRS
system of the type marketed by Dematic Corp. under the Typhoon.RTM.
brand. However, storage module 12 could, alternatively, be a manual type
storage and retrieval system or of the type using inventory holders that
are transported by robotic module drive units. Unit sortation module 18
receives articles retrieved from storage module 12 and sorts those
articles into orders, such as customer orders fulfilled in e-commerce.
The techniques disclosed herein may be used for other applications, such
as retail store fulfillment, and the like.

[0024] In the illustrated embodiment, articles are stored in storage
module 12 in receptacles, such as totes, trays, cartons, or the like, and
are discharged from storage modules on a discharge lane 14 and, when one
or more articles are retrieved from the receptacle, is returned to
storage via a storage lane 16. Such receptacles could each contain an
individual type of article, or stock keeping unit (SKU), or could contain
a heterogeneous mixture of different SKUs.

[0025] A unit induct module 36 receives articles in receptacles retrieved
by the article storage module 12 and inducts the articles. A material
flow system 34 transports articles from unit induct module 36 to
sortation module 18. In the illustrated embodiment, material flow system
34 is an overhead supported pouch system of the type marketed by Dematic
Corp. under the MonaLisa brand or the type marketed by others including
Durkopp Fordertechnik GmbH. However, other types of material flow systems
can be used. Each unit induct module 36 may be an automatic induction
station or manual induct station. Order fulfillment system 10 includes a
plurality of unit induct modules 36 and a plurality of unit sortation
modules 18, wherein material flow system 34 may transport articles from
any one or more of the unit induct modules to any of the unit sortation
modules. As best seen in FIG. 2, this may be accomplished by a matrix 38
of diverters 39. Each of the unit induct modules 36 receives articles
from one or more of the storage modules 12. More than one induct module
36 may be provided for each storage module.

[0026] Order fulfillment system 10 has a control system 20 that includes a
storage module controller 22 and a unit sortation module controller 28
(FIG. 4). Storage module controller 22 and unit sortation module
controller 28 may be logical controllers defined by software or may be
otherwise defined in hardware. Storage module controller 22 has a pending
order queue 24 and a priority policy 25 that opens or activates orders in
queue 24 according to a policy that is selectable by the system operator.
Unit sortation module controller 28 has a pending order queue 30 and a
priority policy 31 that opens orders in the respective pending order
queue 30 according to a policy. Examples of priority policy may be a
combination of order urgency, which is how close an order is to its
desired ship window, and/or order priority, which is how important the
order is and, therefore, should receive expedited processing. Unit
sortation module controller 28 has a work in progress (WIP) controller 32
that limits orders that are active in the unit sortation module to not
exceed a configured capability. Such WIP controller releases a new job
each time a single job is completed. The configured capability of
controller 32 may be configured to the physical capacity of the unit
sortation module but can also be configured to a different value to
achieve different system benefits. For example, the configured capability
can be set below physical capacity of the unit sortation module in order
to provide faster cycle time. Alternatively, the configured capability of
WIP controller 28 can be set above physical capacity of the unit
sortation module for maximum optimization potential.

[0027] Storage module controller 22 may additionally have a work in
progress (WIP) controller 26 that limits orders that are active in the
storage module to not exceed a configured capability. Such configured
capability may be related to the physical capacity of the module and may
be set either at the physical capacity or above or below it. Once the
number of active orders is reached, no additional orders are activated
until orders are completed and the work in progress falls below the
limit. The use of WIP modules activates small amounts of orders, and each
time an order is completed in the module, a new order is added to the
module. This yields fast and predictable order cycle time. This also
reduces the need for buffers throughout conveying system 34.

[0028] Sortation module pending order queue 30 receives orders incoming to
the system 10. Sortation module WIP controller 32 activates orders from
the sortation module pending order queue 30 according to the activation
policy 31 of the sortation module control provided that the order limit
of the sortation module WIP controller is not reached. Having a WIP
controller with unit sortation controller 28 provides a pull-type system.
The storage module pending order queue 24 receives orders that are active
in the sortation module WIP controller 32. The storage module WIP
controller 26 activates orders from the storage module pending order
queue 24 according to the activation policy 25 of the storage module
control provided that the order limit of the storage module WIP
controller is not met. As orders are fulfilled by the storage buffer
module, additional orders may be activated from queue 24. Once an order
is active in storage module WIP controller 26, a retrieval mission is
issued to the retrieval mechanism, such as a shuttle, unit load carrier
or the like. If another order has already requested the same receptacle,
no additional retrieval is necessary. When that receptacle arrives at the
unit induct module 36, all picks for all active orders across all unit
sortation modules 18 will be made from the single receptacle. If all of
the inventory in the receptacle is fully claimed, additional receptacles
will then be retrieved.

[0029] Each unit sortation module 18 supplies an order pack module 40 made
up of a plurality of pack stations 42 and a pack sorter 46. Each pack
station 42 receives a stream of articles making up an order sorted by the
unit sortation module so that an operator, which may be manual or
automated, can pack the articles making up that order. The packed order
can then go directly or indirectly to a shipping subsystem 64 where it is
dispatched to transportation. Pack sorter 46 receives a stream of
articles from the unit sortation module made of the articles for a number
of orders with the articles intermixed for each order. However, no more
orders than the number of pack stations 42 are discharged from the unit
sortation module at a time. As those articles arrive at pack sorter 46,
which is made up of transfer switches 47, the transfer switches
selectively transfers articles to an associated pack station 42. The
articles for an order, which are intermixed with articles for others
arriving at pack sorter 46 are diverted out of the stream of articles to
the pack station. In this manner, the articles for a particular order are
together at the pack station although multiple orders may be backed up
for each pack station. Unit sortation module 18 will not release a stream
of articles for a plurality of orders unless there is room for those
articles at the pack stations and each pack station can only be assigned
one order from a single discharge stream from the unit sortation module.
The sequence of articles at the pack stations will be in order sequence.
However, if an order requires a particular arrangement of items within an
order, such as heavy items first, a separate provision will be required
to provide such arrangement.

[0030] In the illustrated embodiment, each unit sortation module 18 is
made up of a comb sorter 48 having an article input 50 and a plurality of
sorter lanes 52. However other types of unit sortation modules such as a
matrix sorter of the type disclosed in U.S. Pat. No. 5,798,800, the
disclosure of which is hereby incorporated herein by reference in its
entirety, may be used. A diverter 54 at each lane 52 selectively diverts
articles from article input 50 to that lane. An optional buffer 44 may be
provided upstream of article input 50. Optional buffer 44 is a dynamic
buffer that is provided only in case there is a temporary over-feed of
articles to the comb sorter. It performs no part in the organization of
articles into order, but is there to handle any temporary overflow so
that conveyor lines do not need to be shut down if such temporary
overflow should occur. Normally, once a rate of order fulfillment is
exceeded at a unit sortation module, another unit sortation module is
selected and each unit induct module 36 has a path to each unit sortation
module 18. This is accomplished by matrix 38 made up of rows and columns
with diverters 39 at the intersection of each row and column to provide
this ability of each unit induct module to have a path to each unit
sortation module.

[0031] Unit sortation module controller 28 controls comb sorter 48 so that
an order is assigned to one lane 52. However, each lane can receive more
than one order up to a maximum number of orders. The maximum number of
orders that each lane can receive is less than or equal to the number of
pack stations 42, so that the number of pack stations is greater than or
equal to the maximum number of orders that can be received at each
sortation lane 52. Unit sortation module controller 28 assigns activated
orders to a lane 52 until the number of orders in that lane reaches its
maximum number of orders before assigning an activated order to a
different lane 52. All items must be stored in a lane without reaching
its physical capacity or else that order will not be assigned to that
lane. In this event, the sort lane 52 will no longer accept additional
orders and will be ready to release its articles to pack stations. In
order to release a sort lane to the pack stations, the pack stations must
have capacity to accept an additional order for that lane to be released.
The pack stations having the most capacity are selected to receive the
orders from the released sort lane, but with no more than one order going
to any pack station from that release.

[0032] Thus, the order pack modules 40 represent the last process in the
system. The pack station module receives all of the items for a customer
order and facilitates an operator placing them into a shippable container
for the customer. The process flow supports any ratio of unit sortation
modules and order pack modules, and the type of equipment used will
influence the rate. Typically, the unit sortation module will have a much
higher rate than a single order pack module.

[0033] When an order is dispatched from unit sortation module 18 to one of
the pack stations 42, it is subtracted from the number of activated
orders in the unit sortation module in WIP controller 32. Therefore,
another order can be activated. For example, if ten orders are released
from a sort lane 52 to pack stations 42, then ten additional orders can
be activated by WIP controller 32. Information of the ten orders that are
activated by WIP controller 32 is sent to the storage module controller
22 for placement in the pending order queue 24 where they will be
activated by the storage module WIP controller 26 according to activation
policy 25. Activated orders are limited according to the number of
articles in the orders so that fewer large orders may be active than more
small orders.

[0034] Alternatively, a unit sortation module 118 may include an
alternative comb sorter 55. Comb sorter 55 is a two-stage continuous flow
comb sorter. Comb sorter 55 has a first-stage comb sorter 56 and a
second-stage comb sorter 57. Second-stage comb sorter 57 operates in a
similar fashion to comb sorter 48. First-stage comb sorter 56 has an
article input 58, a plurality of sort lanes 60 and diverters 62 that
divert articles from article input 58 to one of lanes 60. Each of lanes
60 can receive a maximum number of orders, but, unlike comb sorter 48,
the maximum number of orders in each sort lane 60 may exceed the number
of pack stations 42. Article input 58 receives articles from a unit
induct module via switch matrix 38 and each sort lane supplies articles
to article input 50 of second-stage comb sorter 57.

[0035] Unit sortation module controller 28 assigns activated orders to one
of lanes 60 until the number of orders in that lane reaches its maximum
number of orders before assigning an activated order to a different sort
lane 60. Once the first articles of an order is assigned to a sort lane
60, all other articles for that order will also be routed to the same
sort lane in first-stage comb sorter 56. This fills a sort lane 60 as
rapidly as possible before assigning other orders to different sort lanes
60 in the first-stage comb sorter. When all of the articles for all of
the orders of a sort lane 60 are present, that sort lane discharges to
second-stage comb sorter 57. Orders are assigned to lanes 52 of comb
sorter 57 in the same manner as to the order assignment for single-stage
comb sorter 48. However, the orders discharged from a sort lane 60 of
first-stage comb sorter 56 may be sent to multiple different lanes of
second-stage comb sorter 57, thus allowing more orders to be assigned to
each sort lane 60 in the first-stage comb sorter than the sort lanes 52
second-stage comb sorter 57 and, hence, more than the number of pack
stations 42. Thus, the option of using a two-stage comb sorter 55 allows
system design which provides scalability without requiring many
additional comb sorter lanes 52 and is not limited by the number of pack
stations 42.

[0036] Simulated responses of an order fulfillment system and method
according to embodiments of the invention for both idealized conditions C
and real world conditions D are shown in FIG. 6. A much greater overlap
between idealized and real world is realized and most orders are
fulfilled within one hour. Very few orders are not fulfilled within an
hour and a half.

[0037] While the foregoing description describes several embodiments of
the present invention, it will be understood by those skilled in the art
that variations and modifications to these embodiments may be made
without departing from the spirit and scope of the invention, as defined
in the claims below. The present invention encompasses all combinations
of various embodiments or aspects of the invention described herein. It
is understood that any and all embodiments of the present invention may
be taken in conjunction with any other embodiment to describe additional
embodiments of the present invention. Furthermore, any elements of an
embodiment may be combined with any and all other elements of any of the
embodiments to describe additional embodiments.